1. Field of the Invention
The present invention relates to a high frequency dielectric ceramic composition, and a dielectric resonator, a dielectric filter, a dielectric duplexer and a communication system using the dielectric ceramic composition.
2. Description of the Related Art
Dielectric ceramics are widely used as dielectric resonators and dielectric filters which are mounted to electronic devices employed in the microwave region millimeter wave region and other high frequency regions, such as in mobile phones, personal radios and satellite receivers. Such high frequency dielectric ceramics must have a high dielectric constant and a high Q value and must have a temperature coefficient of resonant frequency that can be optionally controlled in the vicinity of zero.
As this type of dielectric ceramic compositions, conventionally proposed are, for example, a BaOxe2x80x94Sm2O3xe2x80x94TiO2 based composition (Japanese Unexamined Patent Application Publication No. 57-15309), a BaOxe2x80x94Sm2O3xe2x80x94TiO2xe2x80x94MnO2 based composition (Japanese Unexamined Patent Application Publication No. 59-14214), a BaOxe2x80x94Sm2O3xe2x80x94TiO2xe2x80x94ZrO2 based composition (Japanese Unexamined Patent Application Publication No. 60-3801), and a BaOxe2x80x94Sm2O3xe2x80x94TiO2 based composition (Japanese Unexamined Patent Application Publication No. 6-111624).
However, the BaOxe2x80x94Sm2O3xe2x80x94TiO2 based composition, the BaOxe2x80x94Sm2O3xe2x80x94TiO2xe2x80x94MnO2 based composition and the BaOxe2x80x94Sm2O3xe2x80x94TiO2xe2x80x94ZrO2 based composition respectively disclosed in Japanese Unexamined Patent Application Publications No. 57-15309, No. 59-14214 and No. 60-3801, all exhibit a significantly decreased Q value and the temperature coefficient of resonant frequency (xcfx84f) significantly shifts to the positive or negative side, when the relative dielectric constant (∈r) becomes about 35 to 55. These compositions are therefore disadvantageous in practical use.
The composition disclosed in Japanese Unexamined Patent Application Publication No. 6-111624 attains a high Q value by limiting the compositional proportions of the individual components BaO, Sm2O3 and TiO2. However, the resulting ceramic element made from this composition is liable to invite microcracking due to thermal shock upon soldering and lacks stability of the Q value.
Accordingly, an object of the present invention is to solve the above problems and to provide a high frequency dielectric ceramic composition which has a high relative dielectric constant (∈r) and a high Q value in a microwave region, can control the temperature coefficient of resonant frequency (xcfx84f) in the vicinity of zero (ppm/xc2x0C.) and has a satisfactory thermal shock resistance, as well as to provide a dielectric resonator, a dielectric filter, a dielectric duplexer and a communication system using the dielectric ceramic composition.
Specifically, the present invention provides, in one aspect, a high frequency dielectric ceramic composition. The composition includes, as a main component, a complex oxide containing Ba, Ti and at least one of Sm and Nd as metal elements, and as secondary components, a Mn compound and a Ta compound.
In another aspect, the present invention provides a high frequency dielectric ceramic composition including 100 parts by weight of a main component containing Ba, Ti and at least one of Sm and Nd as metal elements and represented by the following formula:
xBaO-y{(1xe2x88x92xcex1)Sm2O3-xcex1Nd2O3}-zTiO2
wherein x, y, and z are % by mole, and xcex1 is a molar ratio, and x, y, z, and xcex1 satisfy the following conditions: 13xe2x89xa6xxe2x89xa623; 0 less than yxe2x89xa612.; 75xe2x89xa6zxe2x89xa683; 0xe2x89xa6xcex1xe2x89xa61; and x+y+z=100, and, as secondary components, more than 0 and equal to or less than about 0.3 part by weight of a Mn compound in terms of MnO, and more than 0 and equal to or less than about 1 part by weight of a Ta compound in terms of Ta2O5.
The invention provides, in a further aspect, a high frequency dielectric ceramic composition including 100 parts by weight of a main component containing Ba, Ti and Sm as metal elements and represented by the following formula:
xBaO-ySm2O3-zTiO2
wherein x, y, and z are % by mole and satisfy the following conditions: 17xe2x89xa6xxe2x89xa619; 1xe2x89xa6yxe2x89xa66; 77xe2x89xa6zxe2x89xa681; and x+y+z=100, and, as secondary components, more than 0 and equal to or less than about 0.3 part by weight of a Mn compound in terms of MnO, and more than 0 and equal to or less than about 1 part by weight of a Ta compound in terms of Ta2O5.
Of 100% by mole of the Ti element, about 1.5% by mole or less is preferably replaced with Zr.
Preferably, about 50% by mole or less of 100% by mole of the Sm element is replaced with at least one of La, Ce and Pr.
The above dielectric ceramic composition may further include, as a secondary component, about 0.5 part by weight or less of a Nb compound in terms of Nb2O5, relative to 100 parts by weight of the main component.
In yet another aspect, the invention provides a dielectric resonator which is activated by electromagnetic coupling of a dielectric ceramic with an input-output terminal, in which the dielectric ceramic includes the aforementioned high frequency dielectric ceramic composition.
In the dielectric resonator, a copper plating conductor is preferably formed on a surface of the dielectric ceramic.
The present invention further provides a dielectric filter including the dielectric resonator and an external coupling device.
In still another aspect, the present invention provides a dielectric duplexer. The dielectric duplexer includes at least two dielectric filters, input-output connecting devices which are connected to each of the dielectric filters respectively, and an antenna connecting device which is connected to the dielectric filters in common, and at least one of the dielectric filters is the above dielectric filter.
In addition and advantageously, the present invention provides a communication system. The communication system includes the above dielectric duplexer; a transmitting circuit which is connected to at least one input-output connecting device of the dielectric duplexer; a receiving circuit which is connected to at least one input-output connecting device other than the input-output connecting device connected to the transmitting circuit; and an antenna which is connected to an antenna connecting device of the dielectric duplexer.